1. Field of the Invention
The present invention relates to a metal oxygen battery.
2. Description of the Related Art
Metal oxygen batteries have conventionally been known, which have a positive electrode using oxygen as an active substance, a negative electrode using a metal as an active substance, and an electrolyte layer interposed between the positive electrode and the negative electrode.
In the metal oxygen batteries, in the discharge time, a metal is oxidized to form metal ions at the negative electrode, and the formed metal ions permeate through the electrolyte layer and migrate into the positive electrode side. On the other hand, at the positive electrode, oxygen is reduced to form oxygen ions, and the formed oxygen ions bond with the metal ions to form a metal oxide.
In the charge time, at the positive electrode, metal ions and oxygen ions are formed from the metal oxide, and the formed oxygen ions are oxidized to become oxygen. On the other hand, the metal ions permeate through the electrolyte layer and migrate into the negative electrode side, and reduced to become the metal at the negative electrode.
In the metal oxygen battery, if metallic lithium is used as the metal, since the metallic lithium has a high theoretical potential and a large electrochemical equivalent weight, the metal oxygen battery can provide a large capacity. If oxygen in the air is used as the oxygen, since there is no need for filling a positive electrode active substance in a battery, the energy density per mass of the battery can be raised.
However, if the positive electrode is exposed to the atmosphere in order to make oxygen in the air to be a positive electrode active substance, moisture, carbon dioxide and the like in the air invade in the battery, and there is caused a problem of deterioration of the electrolyte, the negative electrode and the like. Then, in order to solve the problem, a metal oxygen battery is known, which has a positive electrode containing an oxygen-occluding material to release oxygen by reception of light, a negative electrode composed of metallic lithium, and an electrolyte layer disposed in a hermetically sealed case, and has a light transmission part to guide light to the oxygen-occluding material (for example, see Japanese Patent Laid-Open No. 2009-230985).
The metal oxygen battery can release oxygen from the oxygen-occluding material by guiding light to the oxygen-occluding material through the light transmission part, and can provide oxygen as a positive electrode active substance without exposing the positive electrode to the atmosphere. Therefore, the deterioration of the electrolyte, the negative electrode and the like due to the invasion of moisture, carbon dioxide and the like into the battery can be prevented.
However, in the conventional metal oxygen battery, the supply of oxygen becomes unstable in the absence of irradiation of light rays, and there is a risk that the light transmission part, which is weaker than other parts of the hermetically sealed case, is broken and the electrolyte solution leaks out. Then, it is conceivable that an oxygen-storing material which does not rely on irradiation of light rays and can occlude and release oxygen chemically, or adsorb and desorb oxygen physically is used as a positive electrode material of the metal oxygen battery. The oxygen-storing material includes YMnO3. 
However, in a metal oxygen battery using an oxygen-storing material composed of YMnO03 as the positive electrode material, the discharge overpotential becomes high, resulting in disadvantages that the charge and discharge efficiency decreases and a high power output cannot be attained.